PROJECT SUMMARY/ABSTRACT Malondialdehyde (MDA) is a ubiquitous and highly reactive end product of non-enzymatic lipid peroxidation, which is a central event in atherogenesis. MDA can covalently modify proteins, and is thought to be pro- inflammatory and atherogenic. It was shown that blood MDA level is correlated to coronary heart disease. However, its exact roles in atherogenesis are unknown as there were no in vivo strategies to specifically neu- tralize it. We recently generated IK17-scFv transgenic mice, which express a single chain variable fragment (scFv) of the human IK17 antibody that targets MDA. My preliminary studies found that IK17-scFv ameliorated Western diet (WD)-induced atherosclerosis in Ldlr-/- mice. MDA staining of lesion cross-sections showed that MDA is enriched in the intima, indicating endothelial cells (ECs) as a major target of MDA. My proposed stud- ies will uncover the mechanisms by which neutralizing MDA decreases atherosclerosis, with an emphasis on EC biology. As the innermost lining of blood vessels, normal ECs are critical for vascular homeostasis and functions. Under physiological conditions, intact ECs maintain an optimal balance between vessel integrity and permeability, exhibit anti-inflammatory function, and maintain normal vascular metabolism. My preliminary studies found that MDA induced excess heme accumulation in EC in vivo, and this was associated with induc- tion in EC of expression of genes encoding heme synthesis enzymes. Unlike its normal functions for oxygen transport and storage, electron transfer or drug metabolism, excess heme causes inflammation and EC dys- function, and increases vascular permeability. Based on my preliminary data, I hypothesize that MDA induces heme accumulation, which promotes endothelial dysfunction during atherogenesis. My proposal will as- sess the pathological effects of the MDA-heme axis on EC dysfunction during atherosclerosis. In Specific Aim1 (K99 phase), I will dissect roles of MDA in EC dysfunction and atherosclerosis using the IK17-scFvLdlr-/- mice. I will also systematically characterize the effects of MDA on EC transcriptome. In Specific Aim2 (R00 phase), I will characterize the effects of MDA on endothelial heme synthesis, and elucidate the underlying mechanisms. In specific Specific Aim3 (K99 and R00 phase), I will generate a new inducible endothelial cell-specific Alas1 (rate-limiting enzyme for heme synthesis) knockout mouse model to study the impact of excess heme on endo- thelial dysfunction and atherosclerosis. The roles of MDA-heme axis in EC dysfunction will be defined in vitro and in vivo. These studies will uncover mechanisms by which targeting MDA and heme can prevent EC dys- function and define novel therapeutic strategies to improve endothelial function and atherogenesis. The out- standing resources and stimulating research environment at UCSD will provide exemplary support for the ap- plicant?s goal of becoming a successful and independent investigator, and the candidate?s mentor has a suc- cessful track record of transitioning trainees into independent faculty. This K99/R00 award will support the ap- plicant toward a tenure track faculty position.